1. Field of the Invention
This invention relates to a flowcell for measurement of fluid sample constituents.
2. Prior Art
Heretofore flowcells for use in continuous-flow analysis have been of the type in which a ray of light is directed transversely through a sample fluid path in a single plane (U.S. Pat. No. 3,518,009) for detection on the opposite side of the path, and of the type such as shown in Bellinger et al U.S. Pat. No. 3,740,158 wherein the sight path is axially along a portion of the fluid path. Commonly, the cross sectional dimension of the fluid path is 1 mm or less which severly limits the cross sectional size of the sight path. In the use of flowcells of the last-mentioned type, a common difficulty has been encountered in the accumulation of debris at the points of the fluid path, coincident with the sight path, where the fluid path enters and leaves the sight path. This debris, which is located where the fluid angularly enters the sight path and leaves it, causes optical noise in sample measurements. Attempts have been made to minimize entrapment of debris, such as small bubbles and dirt, by curving surfaces of the fluid path, as in Isreeli U.S. Pat. No. 3,236,602, or by beveling such surfaces as in Rachlis et al U.S. Pat. No. 3,583,817. Such collection of debris is avoided in Pelavin U.S. Pat. No. 3,418,053 where the fluid path is straight and the light input and output is angled with respect to the path. However, there is a significant light energy loss due to the flowcell structure and such attempts have not been entirely successful. The present invention seeks to obviate these difficulties. Heretofore, as in the last-mentioned structure, attempts have been made to reflect light energy within the flowcell by use of an axially extending silvered or bright surface portion of the cell acting as a mirror reflecting light energy back and forth across the fluid path. However, the significant loss of light energy occassioned by mirror reflections is well known. Further, the length of the sight path is not fixed. Hence, the length of the sight path may be different for different ones of the samples. This gives rise to lack of precision in analysis.
In flowcells, generally, and specifically those utilizing laser illumination, it is old to use total internal reflections for reflection of light energy, such reflections being provided by a polished cell surface. These reflections do not suffer the loss of light energy occassioned by mirror surfaces. The present invention contemplates use of such total internal reflections in a new combination.
Further, attempts are known, as in dye lasers, at multiple pass transverse illumination of a dye path by internal reflections in a dye cell as by Ulrich Fritzler as evidenced in Journal of Physics E: Scientific Instruments, Vol. 7, 1974 printed in Great Britain. However, it is obvious that such attempts were not for the purpose of measurement of a fluid sample constituent and that Fritzler was not faced with the problem of getting light energy out of the cell for detection by a detector.